This invention relates to apparatus and a method for controlling the contents and the filling of a distribution tank for pulverized materials. More particularly, this invention relates to apparatus and a method for controlling the contents and the filling of a distribution tank for pulverized material to deliver the pulverized material under pressure to a shaft furnace, such as, for example, a blast furnace.
Apparatus and methods have previously been proposed for delivering pulverized material, e.g., coal or lignite, to a blast furnace for fuel. Such apparatus and methods involve controlling the contents and the filling of a distribution tank for pulverized materials. The distribution tank operates under pressure and is provided, on its downstream side, with a series of apertures for the extraction of the pulverized material; and the distribution tank is connected, on its upstream side, to an intermediate pulverized material supply tank which serves as an air lock. The intermediate tank is alternately vented and brought under pressure substantially equal to or higher than the pressure in the distribution tank; and it is alternately isolated from and brought into communication with the distribution tank, by operation of two valves.
By way of illustration, but not limitation, apparatus and methods of this type designed for injecting powdered coal or lignite into a blast furnace are disclosed in published European Patent Application Ser. No. 0 021 222 and in U.S. Patent Applications Ser. Nos. 158,612 and 247,511 (all of which are owned by the assignee hereof, and the entire disclosures of which are incorporated herein by reference). In such systems the powdered coal or lignite is extracted through the bottom of the distribution tank by way of the extraction apertures, which may be provided with cellular rotor type blast air locks, and is then carried pneumatically to each of the tuyeres of the blast furnace and injected into the blast furnace.
In order to ensure continuous injection, the level of pulverized material in the distribution tank must be permanently monitored, so that it can be filled when its contents fall below a predetermined minimum. Up to the present time this monitoring has been effected by means of level probes. However, these level probes, for example radiation probes, have the disadvantage of giving only a rather inaccurate indication of the quantity or weight of coal contained in the tank. Since determination of the proper amount of coal to be delivered to the blast furnace is affected by weight, it is desirable that the monitoring of the contents of the distribution tank should also be effected in accordance with the weight of the contents of the distribution tank. This is particularly so, since when monitoring in accordance with the filling level curve, a predetermined maximum or minimum level does not always correspond to the same weight of coal contained in the tank.